Catheters comprise tube-like members inserted into body cavities for diagnostic or therapeutic medical reasons. One of the therapeutic procedures applicable to the present invention is known as percutaneous transluminal coronary angioplasty (PTCA). The first PTCA procedure was developed in approximately 1976 by Dr. Andreas Gruntzig. His fixed wire system features a core or guidewire fixed within a catheter having an inflatable balloon at the distal catheter end with the guidewire stiffening the catheter so that it could be pushed into a desired position in the vascular system. The balloon could be positioned across a blockage and inflated to cause the blockage to be decreased.
If a catheter must be exchanged for a different catheter or one of a different size, a system in which the catheter is inserted over a guidewire is advantageous because the guidewire can be left in place during catheter exchange. The catheter is withdrawn along the guidewire and another catheter is slid into place over the guide wire. Removing the catheter requires removal of the guidewire with possible problems in the guidewire recrossing the stenosis.
Alternatively, a very long "exchange" guidewire, typically about 300 cm long, may be used. Such a long guidewire is difficult and time consuming to handle, requiring two operators and the attendant risk of contamination of the guidewire through contact with objects outside the sterile field. A two-part guidewire may be used instead of the very long guidewire. This arrangement is, however, undesirable because of the additional time required for assembly and the increased thickness that may make smooth exchanges difficult.
Rapid exchange catheters have been developed to eliminate the disadvantages of the long "exchange" wire in over-the-wire systems. These catheters have short guidewire lumens passing through the balloon so that the guidewire exits from the catheter closer to the balloon than to the proximal end of the catheter. This permits the physician to hold the guidewire as he or she removes the catheter with the exchange occurring over the shorter guidewire lumen.
Typical of such rapid exchange catheters are those described by Samson et al. in U.S. Pat. No 4,597,755, by Horzewski et al. in U.S. Pat. No. 4,748,982 and Bonzel in U.S. Pat. Nos. 4,762,129 and 5,232,445. Short guidewire lumens through or along side the balloon are described by Kontos et al. in U.S. Pat. No. 5,180,367. Arrangements for varying the stiffness of catheters in over-the-wire catheters to aid in controlled insertion have been described by Hess in U.S. Pat. No. 4,927,413 and Scopton et al. in WO Patent No. 92/17236. An adjustable stiffness dilation catheter is described by Fugoso et al in U.S. Pat. No. 5,545,138.
While many of these arrangements provide acceptable results when used by a skilled practitioner, problems remain. Many of the multi-lumen catheters, especially those with two lumens, one for movement along a guide wire and the other for balloon inflation liquid and for a variable stiffening wire have an oval or elliptical cross section with a maximum diameter greater than is desirable. Further, the degree of stiffness along different portions of the catheter is not optimum and cannot be varied to the degree desired. Where the distance over which a stiffening wire can be inserted into a catheter is variable, maintaining a particular desired insertion distance is often difficult. Thus, there is a continuing need for improved dilation catheters in which stiffness along the length of the catheter can be varied in a desired and accurately reproducible manner.